1. Field of the Invention
The present invention relates to a reformer, and more particularly, to a reformer having a catalyst capable of performing an auto-thermal catalyst reaction and a steam reforming catalyst reaction according to the type of reaction material introduced into the reforming reactor.
2. Discussion of Related Art
A fuel cell is a power generating system that directly transforms chemical energy into electric energy by an electrochemical reaction between hydrogen and oxygen. In supplying hydrogen to a fuel cell system, pure hydrogen can be directly used, or methanol, ethanol, natural gas or the like can be reformed. Further, in supplying oxygen to the fuel cell system, pure oxygen can be directly used, or oxygen contained in air can be supplied by an air pump or the like.
Meanwhile, the fuel cell is classified into a polymer electrolyte membrane fuel cell (PEMFC) and a direct methanol fuel cell (DMFC), which operate at room temperature or a temperature of less than 100° C.; a phosphoric acid fuel cell (PAFC) which operates at a temperature of 150° C.˜200° C.; a molten carbon fuel cell (MCFC) which operates at a temperature of 600° C.˜700° C.; a solid oxide fuel cell (SOFC) which operates at a high temperature of more than 1000° C.; and so on. These fuel cells operate on basically the same principle, but they are different in the type of fuel, catalyst, and electrolyte utilized.
Among the fuel cells, the polymer electrolyte membrane fuel cell (PEMFC) uses hydrogen obtained by reforming methanol, ethanol, natural gas, etc., and has advantages as compared with other types of fuel cells in that its output performance is very excellent; its operation temperature is low; and its start and response are quickly performed. Thus, the PEMFC can be widely used as a distributed power source for a house or a public building, a small portable power source for a portable electronic apparatus, etc. as well as a transportable power source for a vehicle.
The PEMFC includes a fuel container to store fuel, a reformer to produce hydrogen by reforming the fuel, and an electric generator to generate a voltage and current by an electrochemical reaction between hydrogen and oxygen. The electric generator includes at least one unit cell for generating the electric energy, and the plurality of unit cells can have a stacked structure.
In the PEMFC with this configuration, the fuel stored in the fuel container is supplied to the reformer, the reformer reforms the fuel to produce hydrogen, and the electric generator generates the electric energy by the electrochemical reaction between hydrogen and oxygen.
The reformer not only changes a mixture of the fuel and water into reformed gas containing abundant hydrogen by a reforming reaction, but also removes carbon monoxide included in the reformed gas and capable of poisoning a catalyst of a fuel cell. Thus, the reformer generally includes a reforming reactor to produce the reformed gas containing abundant hydrogen by reforming the fuel, and a CO remover to remove carbon monoxide from the reformed gas. For example, the reforming reactor reforms the fuel into the reformed gas containing abundant hydrogen by a catalyst reaction such as steam reforming (SR), partial oxidation (POX), auto thermal reforming (ATR), etc. Further, the CO remover removes carbon monoxide from the reformed gas by a catalyst reaction such as water gas shift (WGS), preferential CO oxidation (PROX), etc., by refining hydrogen through a separating film, and the like.
The foregoing catalyst reactions can occur under a catalyst activation temperature, and thus a separate heat source is generally provided in the reformer to supply heat to the reformer. In general, the SR catalyst reaction requires a high catalyst activation temperature of 600° C.˜800° C., so that it takes a relatively long time to perform preheating and initial operations. However, hydrogen obtained by the SR reaction has high purity, i.e., contains small impurities such as carbon monoxide. On the other hand, the ATR catalyst reaction is performed by burning the fuel, so that it is possible to use heat generated during the combustion. Thus, it takes a relatively short time to perform preheating and initial operations. However, hydrogen obtained by the ATR catalyst reaction has low purity, i.e., contains a lot of impurities such as carbon monoxide.
According to a conventional reformer, as seen in FIG. 3, heated gas within a heat exchange reformer 4 flows in parallel with the flow of the fuel gas by a controller 5. A first valve A and a second valve B are used as a gas flow direction shifting means. In the case of the endothermic SR reaction, the first valve is open to perform the heat exchange in the inlet side of the reformer so that the fuel gas is heated, thereby enhancing the effect of the SR reaction. On the other hand, the heated gas within the heat exchange reformer 4 flows in a counter direction to the fuel gas supplied by the controller 5 by opening the second valve. This is because the ATR reaction includes an exothermic reaction to upstream fuel gas, and there is an endothermic reaction to downstream fuel gas, and thus the downstream addition enhances the effect of the ATR reaction. To supply the first valve and/or the second valve, the heated gas is generated by burning methanol in a catalyst combustor 3. However, in the conventional reformer, because the heated gas is used for heating the reformer, heat transfer efficiency is likely to be lowered, and the reformer may be contaminated with foreign materials produced after burning methanol.